I just recently discovered cooconjs and i was excited to learn in a week or two. However i also have discovered crosswalk from intel.
Both look very promising And i have no idea which one is better for making games run faster on cellphone.
In article here: https://www.scirra.com/blog/133/introducing-crosswalk-the-new-way-to-publish-to-android it says that it is really fast and asmjs code can actually can get close to native mobile apps. If chrome now can run amsjs compatiable code faster than it should be true..doesn't cooconjs run the chrome version too but without all dom.
First of all, I have developed a game in cocoonjs and it's impressively fast. I would recommend downloading the cocoon launcher from the app/play store. In this app you can open DEMO apps where you can actually see what you can do with cocoonjs and how fast it is.
Secondly what cocoonjs actually did is that they built an complete own accelerated browser from scratch which has 100% focus on speed for the canvas element. This browser is not able to handle any other DOM elements its only for canvas. Nevertheless you can open an transparent webView as a overlay on the accelerated browser which can communicate in both ways. So you are actually able to build a GUI in a normal web browser communicating with the accelerated browser(probably your game) underlying. In addition you can access system functions through their javascript api and there are a lot extension ready to use like facebook/in-app purchase/ads etc all via javascript.
For more information visit http://docs.cocoon.io/